In recent years, printers and copiers have been required to have lower power consumption and higher image quality, so toner has been required to have improved performance. In other words, a toner capable of being fixed at low energy and forming an image having high resistance to external forces, such as rubbing and scratching, has been required. However, there are trade-offs between these properties in typical resins.
To fix toner at low energy, toner is required to have the property of rapidly melting at relatively low temperature. To form images with high resistance to external forces, amorphous elastic resins are required rather than crystalline hard resins.
Thus, the combined use of a resin containing, as a main component, a moiety that has excellent sharp-melting properties and can have a crystalline structure (hereinafter, also referred to as a “crystalline resin”) and an amorphous resin tends to be highly resistant to external forces has been studied. In particular, studies focused on phase-separated structures of crystalline resins and amorphous resins have been reported.
Japanese Patent Laid-Open Nos. 2011-180298 and 6-194874 report toners each having a sea-island structure (matrix-domain structure) in which island portions composed of a crystalline resin are formed in a sea portion composed of an amorphous resin. In this structure, however, the melting properties of each toner as a whole are governed by the amorphous resin constituting the sea portion, thus often failing to provide sufficient sharp-melting properties. When a fixing temperature is increased to the extent that the amorphous resin is melted, the melt viscosity of a binder resin as a whole is excessively reduced, so that a phenomenon in which an image sticks to a fixing device (offset phenomenon) tends to occur.
Japanese Patent Laid-Open No. 59-119362 reports a toner in which a phase-separated structure is controlled by the use of a hydrophilic-hydrophobic polymer compatible with a hydrophobic resin, the toner including a sea portion composed of a low-molecular-weight polyolefin and island portions composed of a hydrophobic polymer. In the foregoing configuration, the entire toner is instantaneously melted in a fixing step. Thus, the configuration has excellent sharp-melting properties. An image formed is mainly composed of a low-molecular-weight wax component and thus tends to have low resistance to external forces. Furthermore, problems with charging characteristics and the preservability of images at high humidity are liable to occur because of the use of the hydrophilic-hydrophobic polymer.
Japanese Patent Laid-Open Nos. 2005-266546 and 2006-84843 report toners each being composed of a crystalline resin as a main component and each having a structure in which a core composed of the crystalline resin is covered with a shell composed of an amorphous resin. In the foregoing configuration, it is possible to obtain the toners that make use of the sharp-melting properties of the crystalline resin. However, an image formed is liable to be damaged from rubbing and scratching because of the crystalline resin serving as a main component. Furthermore, in this configuration, it is difficult to adjust the viscosity of the toners. Thus, it is difficult to achieve both low-temperature fixability and high-temperature offset resistance.
As described above, various phase-separated structures composed of crystalline resins and amorphous resins are devised in toners into which crystalline resins are incorporated. However, a toner capable of being fixed at low energy and providing an image with high resistance to external forces, such as rubbing and scratching, is not yet reported.
The present invention provides a toner in which the conventional problems described above have been solved.
It is an object of the present invention to provide a toner capable of being fixed at low energy and forming an image with high resistance to external forces, such as rubbing and scratching.